The prior art discloses devices which utilize a fuel canister to supply fuel to burners which heat and vaporize an insect repellent composition. The canisters generally contain propane and/or butane under sufficient pressure to liquefy the gases. In order to compensate for variations in vapor pressure, which varies with fuel composition and temperature, these prior art devices use pressure regulators to help control gas flow. Representative devices are described in U.S. Pat. Nos. 4,733,651; 4,759,343; 4,699,123; and 5,700,430; and U.S. patent application Ser. No. 14/848,052 (filed Sep. 8, 2015) and U.S. Provisional Patent Application (filed Feb. 23, 2016) 62/298,539. The contents of these prior patents and applications are incorporated herein by reference in their entireties.
During operation of these prior art devices, when a cartridge containing the gas fuel is inserted into the appliance, the cartridge valve is not opened and fuel does not flow to the pressure regulator. When the appliance is turned on, the regulator pushes a plunger into the cartridge valve, opening it and allowing gas to flow. When a predetermined pressure is reached, the gas acts upon the diaphragm in the regulator to reduce or stop the gas flow by closing the cartridge valve. Thus, while the part of the regulator that senses pressure is in the appliance, the device that controls gas flow is in the valve built into the cartridge. Such a system limits the device to the use of a single attached cartridge.
There are numerous camping stoves in the prior art, for cooking and for heating, which rely on gas supplied by canisters but which do not have a pressure regulator. The gas flow in these devices is user-controlled via needle valves. Some stove models do have regulators, but they still have needle valves for user control of the gas flow.
The combustion devices described above generally must be visually inspected to determine their operating status. If the flame is contained internally, this may involve peering into a view hole to see if a flame or glowing indicator is visible. If there is no visible flame or indicator, it is rarely clear whether gas is flowing into the device. The user is usually reduced to listening closely for the sound of flowing gas, which can be a risky undertaking with a hot device.
Many campers, RV users and backpackers who enjoy the outdoors are subject to insect attacks. The prior devices covered by the above-listed patents are limited to the amount of fuel because of the size of the cartridge. Longer-term use of insect repellent devices powered by a portable fuel source is desirable, for example when users wish to have overnight protection. There remains a need for devices with operating times not limited by the fuel contained in a single canister, for devices which do not require the user to adjust a needle valve to reach and maintain a desired operating temperature, and for devices that clearly indicate their operating status to the user.